1. Field of the Invention
The present invention relates to a magnetic sensor using magnetoresistive elements, such as tunneling magnetoresistive (TMR) elements and giant magnetoresistive (GMR) elements, and a method for manufacturing the magnetic sensor.
2. Description of the Related Art
Heretofore, a magnetic sensor using magnetoresistive elements (GMR elements) which utilize a giant magnetoresistive effect is used as a magnetic sensor for a magnetic encoder for detecting a rotation direction and a rotation angle of a rotor such as a stepping motor. To cause this magnetic sensor to achieve a full 360° sensing capability, a sensor having a configuration in which magnetoresistive elements each have a corresponding one of magnetization directions that are different by 90° is disclosed in Japanese Unexamined Patent Application Publication No. 2009-180604.
As illustrated in FIG. 6, the magnetic sensor disclosed in Japanese Unexamined Patent Application Publication No. 2009-180604 has a configuration in which a magnetoresistive element 102a having a sensitivity axis in a certain direction is formed on a substrate 101 and a first layer is provided by forming an insulating layer 103 on top of the magnetoresistive element 102a. Similarly to the first layer, a second layer is provided by forming a magnetoresistive element 102b and an insulating layer 103, a third layer is provided by forming a magnetoresistive element 102c and an insulating layer 103, and a forth layer is provided by forming a magnetoresistive element 102d and an insulating layer 103. In this case, the magnetization directions of the magnetoresistive elements 102a to 102d are different by 90°.
However, in the magnetic sensor disclosed in Japanese Unexamined Patent Application Publication No. 2009-180604, magnetoresistive elements need to be formed in each layer. In addition, when the magnetoresistive elements 102a to 102d are stacked through the insulating layers 103, differences in height gradually appear by stacking one layer on top of another, causing an influence on the application state of a photoresist. Thus, to avoid the influence on the application state of a photoresist, the magnetoresistive elements need to be disposed separately from each other in plan view. Accordingly, it is not possible for the magnetoresistive elements to be manufactured close to each other, resulting in a constraint on reduction in the size of an element. Furthermore, since the positions in the height direction of the magnetoresistive elements 102a to 102d are different from each other in the magnetic sensor, for example, when a magnetic component is disposed in the upward direction of the plane of FIG. 6 with respect to the magnetic sensor, the distances from the magnetic component to the magnetoresistive elements 102a to 102d are different. Accordingly, sensitivity differences between sensitivity axes may be caused. Moreover, since the positions in the height direction of the magnetoresistive elements 102a to 102d are different from each other in the magnetic sensor, the magnetic sensor has a problem in that routing of wiring lines is difficult and additional processes such as a process of forming contact holes need to be performed, resulting in a complex manufacturing process.